src: update for changed map type in aeson-2

This means that we're now using Data.Map.Strict instead of
Data.HashMap.Strict for JSON objects in general, and specifically
for claims maps and CSV rows.

This addresses certain hash flooding vulnerabilities, but may
have performance downsides.

Compare e.g. https://frasertweedale.github.io/blog-fp/posts/2021-10-12-aeson-hash-flooding-protection.html

src/PostgREST/GucHeader.hs

@@ -5,8 +5,9 @@ module PostgREST.GucHeader
   ) where
 
 import qualified Data.Aeson           as JSON
+import qualified Data.Aeson.Key       as K
+import qualified Data.Aeson.KeyMap    as KM
 import qualified Data.CaseInsensitive as CI
-import qualified Data.HashMap.Strict  as HM
 
 import Network.HTTP.Types.Header (Header)
 
@@ -21,8 +22,8 @@ newtype GucHeader = GucHeader (CI.CI ByteString, ByteString)
 
 instance JSON.FromJSON GucHeader where
   parseJSON (JSON.Object o) =
-    case HM.toList o of
-      [(k, JSON.String s)] -> pure $ GucHeader (CI.mk $ toUtf8 k, toUtf8 s)
+    case KM.toList o of
+      [(k, JSON.String s)] -> pure $ GucHeader (CI.mk $ toUtf8 $ K.toText k, toUtf8 s)
       _ -> mzero
   parseJSON _ = mzero